Which of the following is not a recommended sanitation measure for swimming pool sanitation?

SANITATION MEASURES FOR SWIMMING POOL SANITATION: Recommended area: Recommended area is = 2.2 sq.meter (24 sq.ft) per swimmer Surveillance: Rules and regulation to be posted in appropriate place Filtration of water: Water to be refiltered in less than 6 hours (rapid sand filters); 15% water to be replaced by fresh water everyday Chlorination of water: Residual level of free chlorine to be >1.0 ppm to protect against bacterial and viral agents pH of water: 7.4-7.8 Bacteriological quality of water: To be as close to standards prescribed for drinking water. Ref: Park 25th edition Pgno: 765